1. Field of the Invention
The present invention relates to wired RS system or Radio over Fiber (RoF) communication system and more specifically to a centralized power control method between a Base Station (BS) and Relay Stations (RSs) to improve user fairness and outage probability using a dedicated line and band.
2. Description of the Related Art
In a cellular communication system, throughput and Quality of Service (QoS) per user are major indexes used to determine transmission efficiency. Power control is performed to improve these performance indexes. In particular, by providing uniform receive power to users, an index indicating signal quality, i.e. a Signal to Interference and Noise Ratio (SINR), is maintained as a constant value. Many power control algorithms achieve independent power control for individual Base Stations (BSs) by focusing on power control of each Mobile Station (MS) in a cell.
As illustrated in FIG. 1, a Radio over Fiber (RoF) system can be a cellular system in which a cell is divided into small cells by dividing a service area according to each of BS/Relay Stations (RSs). A plurality of conventional power control algorithms are independently applied in each service area. When a frequency reuse coefficient in a cell is 1, i.e. if the same frequency is used in each service area, MSs, such as an MS A, located in a coverage boundary suffer severe interference due to an interference signal from another service area. When the BS performs power control independently, the BS raises a SINR value by allocating maximum power to the MS A. However, in this case, an amount of interference in service areas of other RSs is increased due to an increase of power from the BS to MS A. In particular, in MSs located in boundaries of other service areas, e.g. an MS B illustrated in FIG. 1, the SINR value is decreased due to an increase of the magnitude of an interference signal. Thus, if the independent power control is performed in service areas of the BS and the RSs without an information exchange between allocated powers, it is limited to improve SINR values of MSs located in boundaries of divided cells.